1. Field of the Invention
This invention relates to an orientation film used in a liquid crystal display device for orienting liquid crystal molecules in a certain direction and also to a process for making such an orientation film. More particularly, this invention relates to an orientation film for a liquid crystal display device, such as twisted nematic (TN) liquid crystal display device, super twisted nematic (STN) liquid crystal display device, ferroelectric liquid crystal display device and super homeotropic (SH) liquid crystal display device, wherein a liquid crystal is intervened between a pair of substrates each having an electrode on a surface facing the liquid crystal, and also to a process for making the same.
2. Description of the Prior Art
A liquid crystal display device having an orientation film of a long-chain polymer having a fluorinated substituent, e.g. a fluoroalkyl chain, is disclosed, for example, by Narita et al in Japanese Patent Laid-open No. 62-174725. This patent application deals with an STN liquid crystal display device which is characterized by using an orientation film consisting of a polyamide- or polyimide-based straight-chain polymer having a fluoroalkyl Chain Of the formula, C.sub.n H.sub.m F.sub.2n+1-m, wherein n is a natural number and m is zero or a natural number not larger than 2n, and liquid crystal molecules having a soft structure. The orientation film in this patent application has the fluoroalkyl group not only in portions directly contacting the liquid crystal, but also in the inside of the orientation film not contacting the liquid crystal and also in the surface of the orientation film contacting the substrate.
Accordingly, the movement of the polymer chain in the orientation film becomes active by heating, so that the density of the fluoroalkyl group in the surface directly contacting the liquid crystal is changed. The change in the surface density of the fluoroalkyl group will vary the orientation of the liquid crystal. The present invention contemplates to provide an orientation film which does not change the orientation of liquid crystals before and after heating.